The goal of this project is to develop a computer-based simulation model which will be a useful aid in the systematic evaluation of evidence, from randomized controlled trials and other sources, on the efficacy and effectiveness of various approaches to colon cancer screening. The model will also be a useful tool for conducting prospective cost-effectiveness analyses of various proposals for implementing colon cancer screening on a mass, population-based level. The goal of the project will be achieved by: l] Designing a structural model to address the complex issues in colorectal cancer screening which arise from the multiplicity of screening modalities, each of which has different characteristics in different regions of the colon, which, in turn correspond to one of two test modalities (e.g. FOBT versus sigmoidoscopy). 2] Constructing a module which models all costs associated with screening, diagnostic follow-up procedures and treatment needs to be developed that is specific to colorectal cancer screening technology. 3] Estimating initial values of model parameters (including distributional specifications), based on a thorough assessment of existing literature and in consultation with NCI. 4] Performing of exploratory calculations with the initial version of the model. Effectiveness, and cost-effectiveness calculations shall be performed for a variety of hypothetical screening scenarios. Results of the modeling exercises shall be compared to the empirical results of RCT screening studies and other clinical studies where possible. Extensive sensitivity analysis shall be performed to identify the parameters that are most crucial in determining the cost-effectiveness results for the various tests.